As explained in Applicant's above identified patent, in response to government rules and regulations and a general desire for safety, rope or cable grabs or similar safety devices have become a requirement for workers working in elevated positions such as on scaffolding or on ladders or the like. Such rope or cable grabs are used in conjunction with a vertical cable or rope which is suspended from a position above the worker to substantially the ground level where it is also secured so as to ensure that the rope or cable is maintained in a vertical position.
Typical rope or cable grabs are used in conjunction with a safety belt or harness which is fastened about the worker. A lanyard is secured to the safety belt or harness and the free end thereof is secured to the rope or cable grab. The lanyard is relative short but is of sufficient length to allow the worker some freedom of movement in horizontal directions. An ideal rope or cable grab should move freely up and down the rope or cable as the worker slowly moves up or down. However, in the event that the worker loses his balance or otherwise is caused to fall, the lanyard causes the rope or cable grab to grip the rope or cable. This breaks the fall by gripping the rope or cable which first slows the worker and eventually stops the fall within several feet.
As is more fully explained in Applicant's prior U.S. Pat. No. 5,156,240 entitled Rope Grab, prior art rope grab devices have proven less than totally acceptable for several different reasons. Some types of rope grabs cannot be attached to or removed from the rope without the necessity of threading the end of the rope through the connector. This is not practical when the suspended rope is several hundred feet long. Hinging and clamping arrangements have been proposed as a solution to this problem but none of them has been found to be entirely satisfactory. The hinged device shown in prior U.S. Pat. No. 4,560,029, for example, has been known to deform upon stopping the fall of a fallen worker which deformation makes it difficult to operate safely thereafter.
Prior known devices and, particularly those of the hinged type, are also not easy to assemble on the rope or cable. Assembly frequently requires a two-hand operation and, quite frequently, a worker working at an elevated position normally only has one hand free.
Another disadvantage found in many conventional rope or cable grab devices is that they cannot be moved freely up or down the rope or cable when the worker moves about. Many of these devices require that the worker hold the device in an open position with a hand grip in order to move the same. This may be difficult when the worker's hands are otherwise occupied. Furthermore, in the event of a fall, the worker may panic and may not release his grip which would cause the rope or cable grab to malfunction and which would, of course, be disastrous to him.
Another serious problem of prior rope grab devices is the manner in which the rope grab grips the rope. The gripping mechanism of most rope grabs includes a cam-lever arrangement wherein a braking cam having teeth or serrated cam surfaces grips the cable. The force at which the cams grab the rope of these prior art devices is directly related to the weight of the worker and the short distance that he free falls before the rope grab is activated. The result is that the sudden stop can injure the worker.
Furthermore, in safety tests required by law or regulations in many jurisdictions, where a weight simulating a worker was dropped a short distance to simulate a fall, the suspended rope which may be a ⅝ or ¾ inch nylon or manila rope was either broken or substantially weakened by the rope grab because of the sudden shock upon it and the cutting of the rope by the braking cams. The Occupational Safety and Health Administration (OSHA) has established standards which must be met for rope grabs and ropes used therewith. These are published at 29 CFR 1910 Appendix C. Many prior art devices, however, are not capable of meeting these requirements.
The rope grab described in Applicant's prior U.S. Pat. No. 5,156,240 is believed to have solved most of the problems of prior art rope grabs and has been commercially successful in the marketplace. It has been found, however, that Applicant's rope grab cannot be used with steel cable due inter alia to the serrated nature of the gripping teeth. While rope is commonly used in indoor environments and for temporary outdoor use, steel cable is required in most outdoor operations in view of the durability of the same.
The primary purpose of the invention described in Applicant's U.S. Pat. No. 5,924,522 was to provide a safety device that could be used with a steel cable since the rope grab of Applicant's U.S. Pat. No. 5,156,240 was not useful with the same. Applicant's improved cable grab has been very successful. However, an additional potential problem has been recognized.
Unlike prior safety devices described above, Applicant's devices (as explained the patents) can move up and down freely under normal conditions. However, should a workman fall, the cable grab slows the fall and then stops it entirely. As explained in the patent, squeezing the cable grab with the workman's hand releases the break. During the beginning of a fall, it is possible for a workman to panic and grab onto the cable grab which would inadvertently release the brake creating a very dangerous situation as the workman may continue to fall.
There is, therefore, a need for a cable grab that will safely and automatically prevent a workman from falling but which cannot be rendered inoperable should a workman intentionally or unintentionally grab onto the same in the event of a fall.